1. Field of the Invention
The present invention relates to the attachment of surgical sutures to surgical needles. In particular, the invention relates to a method and apparatus for the attachment of surgical needles to surgical sutures to provide a combined surgical needle-suture device possessing controlled suture release characteristics.
2. Description of Related Art
For many years, surgeons have employed needle-suture combinations in which a suture or ligature is attached to the shank end of a needle. Such needle-suture combinations are provided for a wide variety of monofilament and braided suture materials, both absorbable and no-absorbable, e.g., catgut, silk, nylon, polyester, polypropylene, linen, cotton, and absorbable synthetic materials such as polymers and copolymers of glycolic and lactic acids.
Needle-suture combinations fall into two general classes: standard needle attachment and removable or detachable needle attachment. In the case of standard needle attachment, the suture is securely attached to the needle and is not intended to be separable therefrom, except by cutting or severing the suture. Removable needle attachment, by contrast, is such that the needle is separable from the suture in response to a force exerted by the surgeon. Minimum acceptable forces required to separate a needle from a suture for various suture sizes are set forth in the United States Pharmacopeia (USP XXII 1990). The United States Pharmacopeia prescribes minimum individual pull-out forces and minimum average pull-out forces as measured for five needle-suture combinations. The minimum pull-out forces for both standard and removable needle-suture attachment set forth in the United States Pharmacopeia are hereby incorporated by reference.
One typical method for securing a suture to a needle involves providing a cylindrical recess in the shank end of a needle and securing a suture therein. For example U.S. Pat. No. 1,558,037 teaches the addition of a cement material to such a substantially cylindrical recess to secure the suture therein. Additional methods for bonding a suture within a needle bore are described in U.S. Pat. Nos. 2,928,395 (adhesives) and 3,394,704 (bonding agents). Alternatively, a suture may be secured within an axial bore in a needle by swaging the needle in the region of the recess, see, e.g., U.S. Pat. No. 1,250,114. Additional prior art methods for securing a suture within a needle bore include expansion of a catgut suture through the application of heat (U.S. Pat. No. 1,665,216), inclusion of protruding teeth within the axial bore to grasp an inserted suture (U.S. Pat. No. 1,678,361) and knotting the end of the suture to be inserted within the bore to secure the suture therein (U.S. Pat. No. 1,757,129).
Methods for detachably securing a suture to a needle are also well known. For example, U.S. Pat. Nos. 3,890,975 and 3,980,177 teach swaging a suture within a needle bore such that the suture has a pull-out value of 3 to 26 ounces. Alternative detachable attachment methods include providing a weakened suture segment (U.S. Pat. No. 3,949,756), lubricant tipping the end of a suture to be inserted in the axial bore of a needle (U.S. Pat. No. 3,963,031) and pretensioning a suture that is swaged within an axial needle bore (U.S. Pat. No. 3,875,946). See also, U.S. Pat. Nos. 3,799,169; 3,880,167; 3,924,630; 3,926,194; 3,943,933; 3,981,307; 4,124,027; and 4,127,133.
Another method for attaching a suture to a needle involves the use of tubing which is secured to the shank end of the needle and to the suture. For example, U.S. Pat. No. 1,613,206 describes the use of a tubing (preferably silver) which is secured to the shank end of a needle and to a ligature. It is suggested that the tube may be attached to the needle by pressure or soldering and to the ligature by pressure or cementing. It is also suggested that the shank of the needle be of reduced cross section and that the furthest extremity of the reduced diameter shank section be provided with a spike or point upon which the suture may be secured prior to the tube application.
U.S. Pat. No. 2,240,330 describes a tubing attachment method whereby the tubing and suture are releasably secured to the needle. In particular, the needle and tubing are provided with cooperating catch and abutment means which are released one from the other by rotating the needle 90.degree. relative to the tubing (or vice versa). The tubing is manufactured from spring-tempered carbon steel or chrome nickel steel and is secured to the suture by heating the tubing and then swaging to the suture.
U.S. Pat. No. 3,311,100 relates to a flexible composite suture having a tandem linkage. The needle is secured to a flexible suture leader manufactured from a readily sterilizable plastic such as nylon, linear polyethylene, isotactic polypropylene, polyester, silk or other proteinaceous material, e.g., by inserting and crimping the leader within an axial bore in the needle shank. The opposite end of the suture leader is crimped within a connector sleeve of a thin walled metal tubing, e.g., stainless steel. The opposite end of the tubing is crimped around a stiff suture, e.g., monofilament stainless steel.
Additional patents which describe the use of tubing to effect suture-needle attachment include U.S. Pat. Nos. 4,672,734 (forming needle from U-shaped metal plate around suture), 4,359,053 (silicone tubing), 3,814,296, 2,802,478 (chamfered tubing ends), 2,302,986, 2,240,330, 1,981,651 (needle and tubing screw threaded), 1,960,117, and 1,591,021.
Commonly assigned, U.S. Pat. No. 5,139,514 describes a combined surgical needle-suture device in which a surgical needle having a shank of reduced cross-section is attached to a suture through a shrinkable tubing, or micro-ferrule, which is fitted about the needle shank and a portion of the suture. Application of energy to the shrinkable tubing brings the tubing into engagement with both the needle shank and the suture. The physical and chemical characteristics of the shrinkable tubing material, the relative diameters of the tubing, the needle shank and the suture, and the amount of energy applied to the tubing may be controlled to provide a needle-suture combination having a desired pull-out force. It is thus possible to produce standard needle-suture combinations and removable needle-suture combinations using a single attachment process and a common inventory of materials.
Minimum average pull-out forces for various sizes of combined surgical needle-suture devices are set forth in the United States Pharmacopeia and are as follows:
TABLE 1 ______________________________________ Average Pull-Out Suture Size Force/Ounces ______________________________________ 8/0 2.39 7/0 3.20 6/0 5.92 5/0 7.97 4/0 15.97 3/0 23.63 2/0 38.80 1/0 52.89 1 63.48 2 and larger 63.48 ______________________________________
U.S. Pat. No. 3,875,946, referred to above, describes needle-suture combinations said to exhibit suture pull-out values that are substantially less than those given by the United States Pharmacopeia as set forth above. According to U.S. Pat. No. 3,875,946, employing the procedure described therein, combined surgical needle-suture devices can be obtained with the following average pull-out forces:
TABLE 2 ______________________________________ Average Pull-Out Suture Size Force/Ounces ______________________________________ 8/0 1-2 7/0 1-3 6/0 2-5 5/0 3-7 4/0 3-15 3/0 3-23 2/0 3-26 1/0 10-26 1 10-26 2 and larger 10-26 ______________________________________
These pull-out forces are obtained by prestressing the suture, i.e., by applying tension to the suture after the tip of the suture has been inserted into an axial bore, or recess, formed in the blunt end of the needle and the needled suture has been swaged so that the force required to pull the suture out of the recess exceeds the minimum limits on needle attachment set forth in the United States Pharmacopeia but is less than the actual tensile strength of the suture used. As the suture is pulled from the needle during application of the tensioning force, the force required to move the end of the suture relative to the needle recess drops to the desired pull-out value, where the tension is released.
A prevailing controlled release needle-suture attachment is a swage or crimp attachment, such as described in the foregoing U.S. Pat. Nos. 3,890,975 and 3,980,177. Swaging dies for achieving removable needle attachment are disclosed in U.S. Pat. Nos. 4,060,885 and 4,072,041. Conventional crimp operations of the type disclosed in these patents are difficult to control. Usually a crimp is created between several dies which close to a fixed gap. Any variation in the crimping dies, the apparatus for closing the dies, the needle size, the hole size, or the suture size will increase variability of the needle suture attachment. Particularly with the manufacture of controlled release sutures, it heretofore has been critical to form the surgical needle to precise dimensions, i.e., the diameter of the needle and the size of the drilled hole may often have to be manufactured within a tolerance of .+-.0.0005 inches to achieve acceptable attachment. Similarly, the suture end to be attached to the needle has to be constructed within similar tight tolerances to assure that the combined tolerances of the suture and needle, when crimped with the crimping die apparatus result in a "pull-out" force within a narrowly defined range. These manufacturing demands result in increased manufacturing time and waste and, hence, increased cost to the manufacturer.
In addition, conventional crimping operations often distort the end of the needle thereby causing it to lose its symmetry. This is undesirable because it may result in an unacceptable pull-out force or increased trauma to tissue when the non-symmetrical needle is drawn through the tissue.
For example, one conventional crimping method requires that the back end of the needle be struck with two opposed dies. The needle is then rotated 90.degree. and the dies are arranged to strike the needle a second time. In effect, the first strike changes a round hole into one of elliptical shape, i.e., major and minor axes. The act of rotating the needle 90.degree. and repeating the operation to some extent completes the attachment. However, these procedures increase handling during manufacture and the likelihood that unacceptable attachment will be achieved. Indeed, rotating the suture and needle before the attachment is complete is likely to dislodge the suture tip in whole or part prior to completion of the attachment, resulting in unacceptable attachment. Moreover, multiple opposing die hits may produce a distorted needle end which results in corresponding asymmetry of tissue apertures and trauma during use.
In addition to size effects, the surface smoothness of the suture and the needle aperture, and the presence of any lubricants applied to either the suture or the needle may affect the resulting pull-out values. The conventional method of crimping, as described, underscores many of these parametric inconsistencies and necessarily utilizes multiple hits to overcome these process variabilities.
Commonly assigned U.S. Pat. Nos. 5,046,350 to Proto et al. and 5,099,676 to Proto et al. disclose crimping or swaging die configurations for attaching surgical needles and sutures. The split ring die disclosed in the U.S. Pat. No. 5,046,350 includes a relief zone defined between a pair of extensions. A needle positioned between a pair of the split ring dies is stricken by the extensions whereby the superfluous material caused by the swaging action collects within the relief zone. The novel configuration of the split ring die provides a more uniform swage while the needle retains its circular symmetry in the area of suture attachment.
U.S. Pat. No. 5,099,676 discloses a die featuring a novel clover leaf shape which is defined by a generally circular surface having a series of interconnected alternating individual convex and concave curved surfaces. The convex and concave surfaces permit needle material swaged during the crimping process to flow from the convex portions which perform the actual crimping action to the concave areas so as to collect within the concave portions. The clover leaf dies provide unique attachment of the suture components and also maintains the symmetry of the product.
The present invention is directed to a unique die arrangement and the swage formed thereby which overcome the inherent disadvantages associated with conventional crimping dies and processes, particularly applied to a suture needle to achieve removable needle-suture attachment. In accordance with the method and apparatus of the present invention, attachment is achieved while retaining the symmetry of the needle. A significant advantage of the method and apparatus of the present invention resides in the fact that the needle-suture components need not be manufactured to as strict tolerances in order to achieve consistent attachment and pull-out force. In addition, the method and apparatus for attaching needles to sutures requires less handling of the suture and needle and reduces process control requirements.